Twitter CEO Dick Costolo told a London audience earlier this week that the microblogging service is now processing half a billion tweets a day, according to a published report.

According to V3, Costolo, speaking at the Internet Advertising Bureau's Engage conference in the U.K. capital, revealed the half-billion number, which is up from 400 million daily tweets, the last official number Twitter had publicized.

In the same talk, Costolo also confirmed recent reports that Twitter is testing out "like" and star buttons to potentially replace the "favorite" tool the service has used for years. The Next Web had originally reported that the service was experimenting with that change.

Until now, the company had declined to comment on the issue. And it did not immediately respond to a request for comment on Costolo's reported remarks in London.